Conservative MPs have demanded an apology from Labour's candidate for London mayor, Ken Livingstone, after an interview in which he said their party was "riddled" with homosexuals and claimed Baroness Thatcher was "clinically insane" while prime minister.

Mr Livingstone told the New Statesman that some Tory MPs were hypocritically denouncing homosexuality, while secretly "indulging".

But he said that by contrast, since the leadership of Tony Blair, being gay or lesbian had been a boon to Labour MPs' careers.

Discussing the issue of privacy with the magazine's associate editor Jemima Khan, Mr Livingstone said: "(The public) should be allowed to know everything, except the nature of private relationships - unless there is hypocrisy, like some Tory MP denouncing homosexuality while they are indulging in it."

Asked why he referred particularly to Conservative MPs, he added: "Well, the Labour ones have all come out. As soon as Blair got in, if you came out as lesbian or gay you immediately got a job. It was wonderful.

"You just knew the Tory party was riddled with it like everywhere else is."

Conservative London MPs Angie Bray and Mike Freer wrote to Labour leader Ed Miliband calling on him to ensure that the remarks were retracted.

Ms Bray said: "These are the sort of offensive remarks we hear all too often from Labour's candidate for mayor. Ed Miliband should condemn these outrageous comments and get him to apologise immediately."

A spokesperson for Ken Livingstone said: "Ken is clearly saying the advance of lesbian and gay people into politics is unequivocally a good thing.

"He has fought for equality for gay and lesbian people throughout his life, and the fact they are represented in all major political parties is a sign of the progress that has been made."